Known cooling systems in oil sands froth treatment process included open loop once-through cooling systems and conventional closed cooling water loop systems where process exchangers transfer heat to circulating cooling water which then recovers with heat exchangers higher grade heat to a recycling process water stream and then removes the low grade heat by evaporative cooling in a cooling tower.
Open loop cooling systems that transfer process heat directly have poor energy efficiency and are not environmentally acceptable. Within oil sand operations, bitumen extraction process requires significant volumes of hot process water at or around 80° C., some of the heat being largely recovered for recycling at temperatures ranging between 4° C. to 30° C. depending on factors such as season and pond size. This recycle water contains suspended solids, hydrocarbon e.g. bitumen, various salts e.g. chlorides and minerals that cycle up over time to reflect connate water contaminates in the ore body, and as exposed to atmosphere the water is saturated with both oxygen and carbon dioxide gases. Various oil sands operators have used this recycle water stream as cooling water with costly repercussions and drawbacks including: frequent need to clean fouled exchangers and to permit continuous exchanger cleaning have spare exchangers installed; upgrading of metallurgy to combat erosion and corrosion particularly in situations where the process cooling temperatures are above 60° C.; frequent need to maintain exchanger velocities to control fouling; piping repairs on an on-going basis due to erosion and corrosion due to oxygen, chlorides and temperatures; and temperature limitations forcing supplementary heating of process water for extraction operations.
Oil sand operators have also used some conventional close loop cooling systems using cooling towers to reject heat by evaporative cooling with make-up water from the river. This option is not without challenges. For instance, the evaporative process causes minerals in make-up water to cycle up to saturation levels which if not managed will foul exchangers. The management involves blow down and make-up inventories together with chemical anti-scaling programs. Despite this water treatment and management, maximum cooling water temperatures are limited to levels similar to recycle water at about 65° C. In addition, the location of the cooling tower can create significant fog and ice safety issues. Consequently, towers are generally placed a significant distances from process unit and the interconnect supply and return pipelines are relatively costly and also often have diameters from 24-60 inches. Furthermore, the heat lost by evaporative cooling is not available for process use. In addition, blow down with concentrated minerals are disposed in tailing systems. Divalent ions, such as calcium ions, adversely affect bitumen extraction if not precipitated by carbon dioxide.
In addition, integrating froth treatment plant with other oil sands process operations in fraught with challenges due to differing operational and upset conditions.
In summary, known practices and techniques for heat exchange and cooling in this field experience various drawbacks and inefficiencies, and there is indeed a need for a technology that overcomes at least some of those drawbacks and inefficiencies.